Inflatable packer

ABSTRACT

An improved inflatable packer is provided. In one embodiment, the improved packer has a tubular mandrel with an outer diameter essentially equal to the deflated inner diameter of an inflatable element surrounding the mandrel and has fluid flow passages that are adapted to cause at least a portion of pressurized fluid for inflating the element to be introduced into the annular space between the packer and the mandrel in a direction substantially parallel to the longitudinal axis of the tubular mandrel.

FIELD OF THE INVENTION

This invention relates generally to an improved inflatable packer usefulfor restricting flow of fluids in a wellbore during the perforating andtreating of a subterranean formation to increase the production of oiland gas therefrom. More particularly, this invention relates to aninflatable packer having a tubular mandrel with an outer diameteressentially equal to the deflated inner diameter of an inflatableelement surrounding the mandrel and further having fluid flow passagesthat direct the flow of fluid for inflating the element into and throughthe annular space between the mandrel and the element. Preferably, thefluid flow passages direct the flow of fluid for inflating the elementin a direction substantially parallel to the longitudinal axis of themandrel.

BACKGROUND OF THE INVENTION

When a hydrocarbon-bearing, subterranean reservoir formation does nothave enough permeability or flow capacity for the hydrocarbons to flowto the surface in economic quantities or at optimum rates, hydraulicfracturing or chemical stimulation is often used to increase the flowcapacity. A wellbore penetrating a subterranean formation typicallyincludes a metal casing cemented into the original drill hole.Perforations are made to penetrate through the casing and the cementsheath surrounding the casing to allow hydrocarbon flow into thewellbore and, if necessary, to allow treatment fluids to flow from thewellbore into the formation.

Hydraulic fracturing comprises injecting fluids (usually viscous shearthinning, non-Newtonian gels or emulsions) into a formation at pressuresand rates high enough to cause the reservoir rock to fail and to form aplanar, typically vertical, fracture (or fracture network) much like thefracture that extends through a wooden log as a wedge is driven into it.Granular proppant materials, such as sand, ceramic beads, or othermaterials, are generally injected with the later portion of thefracturing fluid to hold the fracture(s) open after the fluid pressureis released. Increased flow capacity from the reservoir results from theflow path left between grains of the proppant material within thefracture(s). In chemical stimulation treatments, flow capacity isimproved by dissolving materials in the formation or otherwise changingformation properties.

Application of hydraulic fracturing as described above is a routine partof petroleum industry operations as applied to individual target zonesof up to about 60 meters (200 feet) of gross, vertical thickness ofsubterranean formation. When there are multiple or layered reservoirs tobe hydraulically fractured, or a very thick hydrocarbon-bearingformation (over about 60 meters), then alternate treatment techniquesare required to obtain treatment of the entire target zone.

When multiple hydrocarbon-bearing zones are stimulated by hydraulicfracturing or chemical stimulation treatments, economic and technicalgains are realized by injecting multiple treatment stages that can bediverted (or separated) by various means, including mechanical devicessuch as bridge plugs, packers, downhole valves, sliding sleeves, andbaffle/plug combinations; ball sealers; particulates such as sand,ceramic material, proppant, salt, waxes, resins, or other compounds; orby alternative fluid systems such as viscosified fluids, gelled fluids,foams, or other chemically formulated fluids; or using limited entrymethods.

In mechanical bridge plug diversion, for example, the deepest intervalis first perforated and fracture stimulated, then the interval istypically isolated by a wireline-set bridge plug, and the process isrepeated in the next interval up. Assuming ten target perforationintervals, treating 300 meters (1,000 feet) of formation in this mannerwould typically require ten jobs over a time interval of ten days to twoweeks with not only multiple fracture treatments, but also multipleperforating and bridge plug running operations. At the end of thetreatment process, a wellbore clean-out operation would be required toremove the bridge plugs and put the well on production. The majoradvantage of using bridge plugs or other mechanical diversion agents ishigh confidence that only the target zone is treated, and thestimulation is diverted from previously treated zones. The majordisadvantages are the high cost of treatment resulting from multipletrips into and out of the wellbore and the risk of complicationsresulting from so many operations in the well. For example, a bridgeplug can become stuck in the casing and need to be drilled out at greatexpense. A further disadvantage is that the required wellbore clean-outoperation may damage some of the successfully fractured intervals.

To overcome some of the limitations associated with completionoperations that require multiple trips of hardware into and out of thewellbore to perforate and stimulate subterranean formations, methods andapparatus have been proposed for “single-trip” deployment of a downholetool string to allow for fracture and chemical stimulation of zones inconjunction with perforating. Specifically, these methods and apparatusallow operations that minimize the number of required wellboreoperations and time required to complete these operations, therebyreducing the stimulation treatment cost. Frequently, an inflatablepacker assembly is included in a tool string used for these types ofapplications.

Referring now to FIG. 1 (PRIOR ART), a standard inflatable packerassembly 10 comprises several separate parts, including an inflatableelement 14, a tubular mandrel 12, two end-caps 13, and two ends 16 and18. Often, end 16 is fixed and end 18 is sliding, i.e., adapted to slidealong mandrel 12 as element 14 is inflated and/or deflated, as will befamiliar to those skilled in the art. The packer assembly is typicallyattached to tubing 17. There are three categories ofcommercially-available, inflatable elements: metal-slat reinforced,metal-cable reinforced, and polymer composite reinforced. An inflatablepacker can be assembled using any type of inflatable element, includingthe three described above, by inserting a mandrel through the center ofthe element and using two end-caps to attach the element to the mandrel.

Currently, the elements that have the most desirable properties in termsof absolute pressure resistance and internal differential-pressureresistance, comprise an outer elastomeric cover (which, when inflatedand sealingly engaged with the wall or casing of the wellbore, providespressure seals above and below the packer), a reinforcement structure(which provides adequate mechanical strength to withstand stressesinduced by inflation), and an internal elastomeric bladder (whichprovides a pressure seal between the fluids inside and outside theelement). The combination of high pressure resistance, sufficientthermal stability, and thin cross-section has allowed thesecover-reinforcement-bladder composite elements to essentially dominatethe oil-field market.

As each type of reinforced element has different strengths andweaknesses, each type is generally best suited for particular types ofapplications. Commercially available polymer-reinforced packers are mostoften used in low temperature and/or low pressure water wellapplications and can typically survive many inflation/deflation cyclesunder lower pressure conditions. Metal-cable reinforced packers havealso been optimized to maximize fatigue life (and hence the number ofinflation/deflation cycles), and while testing has shown that currentlyavailable varieties may not handle as many cycles as thepolymer-reinforced variety, they are currently able to handle relativelyhigh temperatures. Lastly, metal-slat reinforced elements have beenoptimized for high-pressure, high-temperature service at the cost ofshorter fatigue life.

All three varieties of packers are typically exposed to serviceconditions that place the mandrel of the packer in tension. Recentextension of these packers to newly developed completion techniques, forexample, as described in U.S. Pat. Nos. 6,394,184 and 6,520,255, and inU.S. Publication No. 2003/0051876, which deal with a technology known as“Annular Coiled Tubing Fracturing” or “ACT-Frac”, require that thepackers withstand much higher compressive loads than currently availablepackers can withstand without buckling the mandrel. Existing partialsolutions to large compressive loads include the use of a largerdiameter inflatable element with a correspondingly larger mandrel, theuse of cement as an inflation fluid, and alternate designs to thetool-string to reduce the effective compressive loads, such as byadjusting the position of the element within the tool-string. Each ofthese partial solutions introduces additional drawbacks. The use of alarger diameter element reduces the clearance between the outer diameterof the element and the inner diameter of the casing, which decreases thecross-sectional area between the element and the casing. This reducesthe maximum running speeds and increases the chance for damaging theelement or sticking the tool downhole. Inflating the element with cementor other hardening material supports compressive loads extremely wellbut does not allow for the multiple inflation/deflation cycles requiredby some applications. Lastly, placing the element in a differentposition within a string of tools to reduce compressive loading may bedetrimental in several ways, including shifting the higher compressiveloads to other tools, exposing other downhole tools toflows/environments otherwise protected by the packer, making thetool-string more complex, or changing the functionality of thetool-string itself.

Using a larger mandrel without increasing the diameter of the inflatableelement is also an option, but raises other concerns. In packer designsthat use the gap between the mandrel and the element to inflate ordeflate the element, increasing the diameter of the mandrel results in asmaller inflation/deflation pathway and increases the likelihood thatthe rubber interior of the element will pinch off flow to the inflationchamber. Operational problems will arise if the flow blockage results ineither a partial inflation (e.g., lack of pressure isolation in thewellbore) or partial deflation (e.g., the packer is more likely tobecome stuck in the wellbore, the outer cover is more likely toexperience additional wear, and the element is more likely to experiencepinching failures). Despite these problems, however, larger mandrels areoccasionally used for either their mechanical strength/bucklingresistance, or to allow for a larger passageway through the interior ofthe mandrel. Towards this end, two techniques have arisen to alleviateflow restrictions through the mandrel-element gap.

One technique utilizes a plurality of holes drilled through the entirecovered length of the mandrel thereby affording multiple fluid pathwaysbetween an energized fluid source within the mandrel and the inflationchamber. Unfortunately, for several tool designs and completionprocedures, it is undesirable to have the inflation fluid pathwayinclude the interior of the mandrel (which may be required to containelectric lines or serve as a passageway for a separate fluid system). Inaddition, the holes can result in internal-bladder failure initiationsites due to either external pressure extrusion through the holes orjet-impingement onto the bladder during inflation. A second technique,which does not use the interior of the mandrel in the inflation fluidpathway, requires a second, concentric, perforated tube between theelement and a solid mandrel (see U.S. Pat. No. 5,495,892). The inflationpathway is then shifted to between the mandrel and the concentric tube,effectively preventing the element from pinching off theinflation/deflation fluid pathway. However, this design is notapplicable in situations where the mandrel is placed under largercompressive stresses, as the additional tube can not be load bearingwhen used in floating head packers (i.e., inflatable packers that useone fixed end and one floating end, i.e., an end that is allowed totravel during inflation (the predominant packer design in theoil-field)). Moreover, the perforated concentric tube requiresadditional space which must translate into either a larger elementdiameter (less wellbore-element clearance), a smaller mandrel diameter(less buckling resistance), or a thinner element design (lower pressureresistance).

Inner-bladder failures are the most common failure mechanism incomposite packers. This is not surprising as these bladders tend to beconstructed of thin elastomeric tubes (necessary to allow expansionduring inflation) and they are typically the only pressure seal aroundthe inflatable chamber. Two of the most common inner-bladder failuremechanisms are pinching failures and extrusion failures. Pinchingfailures initiate during deflation when the thin elastomeric bladder,having just been stretched during the inflation stage, is now quicklyforced into its initial deflated dimensions without giving the elastomerenough time to relax. To accommodate a smaller diameter in less timethan the elastomer requires to relax, the still distended bladder canfold over itself given enough radial clearance. If a large external orinternal pressure is applied to the packer element while a fold ispresent, the pressure can act to squeeze the fold together and split thebladder along the fold line. Once the bladder splits, the element nolonger possesses pressure integrity and the packer has failed. A smallerclearance between the mandrel and the element would alleviate thisproblem, but can result in other problems as stated above.

Extrusion failures occur when applied pressure forces the thinelastomeric bladder through a gap or hole in either the surroundingreinforcement structure or the mandrel/mandrel-end-cap junction. To helpprevent internal-pressure related extrusion failures, element design hasfocused on minimizing the gap-sizes in the element reinforcingstructures wrapped around the inner bladder. How effective the design isin minimizing the reinforcement gap size, coupled with the strength ofthe reinforcement, generally determines the maximum internal pressuredifferential that the element will be able to resist without failure.However, the same degree of care has not been extended to preventingextrusion failures caused by large applied external pressures. This isin part due to the relatively low frequency of events with large appliedexternal pressures. Large external pressures can arise inadvertently(e.g., well control events, greater than anticipated reservoirpressures, human or mechanical error, etc.) or be applied on purpose(e.g., standard wellbore or lubricator pressure tests, stimulationprocedures, production, well tests, etc.). With the extension ofinflatable packers to high pressure stimulation operations, thelikelihood that packers will experience higher external pressures isincreased; thereby requiring packers with improved external pressureresistance. Improved external pressure resistance will permitapplication of inflatable packers to a wider range of newly developedcompletion operations, allow the packers to be present in the wellboreor lubricator during pressure testing, and allow the packer to remain inservice after an unexpected external pressure event. The inner-bladdersare especially susceptible to external pressure extrusion failures whenthe element is in a deflated, non-sealing state because theinner-bladder is in direct contact with any holes or gaps in the mandrelassembly.

Inflatable packers are rarely used in conjunction with proppantfracturing operations due to their propensity to become damaged or stuckdownhole when exposed to particulate-laden environments. Current designsgenerally rely on single o-ring seals to provide both static and dynamicpressure seals at the mandrel/end-cap junction to isolate thepressurized, inflatable chamber from the wellbore. Through testing, wehave found that, under both particulate-free and particulate-ladenenvironments, more robust pressure seals would be advantageous. Inaddition to seal design, the design of the outer elastomeric cover usedin currently available packers also can led to poor performance inparticulate-laden environments. The ability of the packer to return toits original outer diameter after each inflation maximizes thecross-sectional area in the annulus between the packer and the wellbore.This large annular area increases the ability of particulate-laden fluidto flow past the packer after each set, consequently reducing thelikelihood of not being able to move the packer in the wellbore.

Extensive testing of commercially available, inflatable packers revealedseveral limitations in existing packer designs, including the inabilityof these packers to resist bending and buckling under appliedcompressive loads, to resist extrusion and pinching failures of theelement bladders, to perform in particulate-laden environments, and tohave large annular clearance when deflated. With the development of theabove-referenced completion technologies, there is now a need for animproved inflatable packer that possesses high buckling resistance,improved inner-bladder failure resistance, improved inflation-cyclerepeatability, better resistance to particulate damage, a large tubularmandrel inner diameter through which fluids and electrical conduits canbe passed, and a minimal deflated outer diameter to minimize therestriction to annular flow.

Therefore, an object of this invention is to provide such improvedinflatable packers. Other objects of this invention will be madeapparent by the following description of the invention.

SUMMARY OF THE INVENTION

An inflatable packer is provided that comprises: (a) a tubular mandrelhaving a longitudinal axis; (b) an inflatable element substantiallyconcentrically disposed around said mandrel, said element having a firstend and a second end with each said end being sealingly attached to themandrel, and said element being adapted (i) to be inflated byintroduction of pressurized fluid into an annular space between saidelement and the mandrel and (ii) to be deflated by removal of saidpressurized fluid from said annular space; and (c) one or more fluidflow passages extending through the annular space between the elementand the mandrel, which fluid flow passages are adapted to cause at leasta portion of said pressurized fluid to be introduced into said annularspace in a direction substantially parallel to said longitudinal axis ofsaid tubular mandrel. In one embodiment, each of said fluid flowpassages is in fluid communication with each of the other said fluidflow passages. In one embodiment, the mandrel has an outer diameter thatis substantially equal to the inner diameter of the element prior toinflation. In one embodiment, at least one of the fluid flow passages isformed by two or more grooves in the mandrel. In another embodiment, theelement comprises an outer elastomeric cover and a plurality ofinterconnected inner slats and, further, at least a portion of saidelastomeric cover has been removed such that at least a portion of theinterconnected inner slats are exposed.

In another embodiment, an inflatable packer suitable for use under apre-selected compressive load is provided, wherein the inflatable packercomprises: (a) a tubular mandrel having a longitudinal axis, and (b) aninflatable element substantially concentrically disposed around saidmandrel and adapted to provide pressure seals above and below saidinflatable packer when inflated, and further said mandrel has an outerdiameter suitably large to prevent bending and buckling of the mandrelunder said pre-selected compressive load that results in failure ofeither of said pressure seals or of said inflatable packer.

In another embodiment, an inflatable packer suitable for use under apre-selected external pressure is provided, wherein said inflatablepacker comprises: (a) a tubular mandrel having a longitudinal axis; (b)an inflatable element comprising an inner bladder and an outerelastomeric cover and being substantially concentrically disposed aroundsaid mandrel, said element having a first end and a second end with eachsaid end being sealingly attached to the mandrel, and said element beingadapted (i) to be inflated by introduction of pressurized fluid into anannular space between said element and the mandrel and (ii) to bedeflated by removal of said pressurized fluid from said annular space;(c) one or more fluid flow passages extending through the annular spacebetween the element and the mandrel, which fluid flow passages areadapted to cause at least a portion of said pressurized fluid to beintroduced into said annular space in a direction substantially parallelto said longitudinal axis of said tubular mandrel, and further whereinsaid mandrel has an outer diameter suitably large to prevent extrusionof said inner bladder into one or more of said fluid flow passages in adirection substantially parallel to said longitudinal axis of saidtubular mandrel when said packer is subjected to said pre-selectedexternal pressure. In one embodiment, each of said fluid flow passagesis in fluid communication with each of the other said fluid flowpassages.

In another embodiment, an inflatable packer is provided that comprises:(a) a tubular mandrel having a longitudinal axis, and (b) an inflatableelement comprising an inner bladder and an outer elastomeric cover andbeing substantially concentrically disposed around said mandrel, saidelement having a first end and a second end with each said end beingsealingly attached to the mandrel, and said element being adapted (i) tobe inflated by introduction of pressurized fluid into an annular spacebetween said element and the mandrel and (ii) to be deflated by removalof said pressurized fluid from said annular space, and further whereinsaid mandrel has an outer diameter suitably large to prevent folding ofsaid inner bladder within said annular space between said element andsaid mandrel.

In another embodiment, an inflatable packer is provided that comprises:(a) a tubular mandrel having a longitudinal axis, and (b) an inflatableelement comprising an outer elastomeric cover and a plurality ofinterconnected inner slats and being substantially concentricallydisposed around said mandrel, said element having a first end and asecond end with each said end being sealingly attached to the mandrel,and said element being adapted (i) to be inflated by introduction ofpressurized fluid into an annular space between said element and themandrel and (ii) to be deflated by removal of said pressurized fluidfrom said annular space, and further wherein at least a portion of saidelastomeric cover has been removed such that an appropriate length ofsaid interconnected inner slats are exposed to minimize the deflateddiameter of said element and to prevent loss of said outer elastomericcover when said packer undergoes a plurality of inflation/deflationcycles. In one embodiment, a plurality is meant to include two or moreinflation/deflation cycles. In another embodiment, a plurality is meantto include three or more inflation/deflation cycles. In yet anotherembodiment, a plurality is meant to include five or moreinflation/deflation cycles.

In another embodiment, an inflatable packer suitable for use under apre-selected internal pressure is provided, wherein said inflatablepacker comprises: (a) a tubular mandrel having a longitudinal axis, and(b) an inflatable element comprising an outer elastomeric cover, aninner bladder, and a plurality of interconnected inner slats and beingsubstantially concentrically disposed around said mandrel, said elementhaving a first end and a second end with each said end being sealinglyattached to the mandrel, and said element being adapted (i) to beinflated by introduction of pressurized fluid into an annular spacebetween said element and the mandrel and (ii) to be deflated by removalof said pressurized fluid from said annular space, and further, whereina portion of said elastomeric cover has been removed such that anappropriate length of said interconnected inner slats are exposed toprevent said exposed slats from damaging said inner bladder when saidpacker is subjected to said pre-selected internal pressure.

In another embodiment, an inflatable packer suitable for use under apre-selected external pressure is provided, wherein said packercomprises: (a) a tubular mandrel having a longitudinal axis; (b) aninflatable element comprising an inner bladder and an outer elastomericcover and being substantially concentrically disposed around saidmandrel, said element having a first end and a second end with each saidend being sealingly attached to the mandrel, and said element beingadapted (i) to be inflated by introduction of pressurized fluid into anannular space between said element and the mandrel and (ii) to bedeflated by removal of said pressurized fluid from said annular space;and (c) one or more fluid flow passages extending through the annularspace between the element and the mandrel, which fluid flow passages areadapted to cause at least a portion of said pressurized fluid to beintroduced into said annular space in a direction substantially parallelto said longitudinal axis of said tubular mandrel, and wherein at leastone of said fluid flow passages has at least one edge that is chamferedat an angle of about 40 degrees to about 50 degrees. In one embodiment,said at least one edge is chamfered at an angle of about 45 degrees.

In another embodiment, an inflatable packer suitable for use under apre-selected external pressure is provided, wherein said inflatablepacker has a fixed end and a floating end and comprises: (a) a tubularmandrel having a longitudinal axis; (b) an inflatable element comprisingan inner bladder and an outer elastomeric cover and being substantiallyconcentrically disposed around said mandrel, said element having a firstend and a second end with each said end being sealingly attached to themandrel, and said element being adapted (i) to be inflated byintroduction of pressurized fluid into an annular space between saidelement and the mandrel and (ii) to be deflated by removal of saidpressurized fluid from said annular space; (c) one or more fluid flowpassages extending through the annular space between the element and themandrel, which fluid flow passages are adapted to cause at least aportion of said pressurized fluid to be introduced into said annularspace in a direction substantially parallel to said longitudinal axis ofsaid tubular mandrel; and (d) at least one device adjacent said fixedend, said device being adapted to prevent extrusion of said innerbladder into one or more of said fluid flow passages in a directionsubstantially parallel to said longitudinal axis of said tubular mandrelwhen said packer is subjected to said pre-selected external pressure.Said device that is adapted to prevent extrusion of said inner bladderwhen said packer is subjected to said pre-selected external pressure maycomprise a filter, a screen, or any other device capable of preventingsuch extrusion, as will be familiar to those skilled in the art.

DESCRIPTION OF THE DRAWINGS

The advantages of the present invention will be better understood byreferring to the following detailed description and the attacheddrawings in which:

FIG. 1 (PRIOR ART) is a sketch of a standard inflatable packer assembly;

FIG. 2A is a cut-away view of an inflatable packer according to thisinvention;

FIG. 2B is a plan view at section 24 of the inflatable packerillustrated in FIG. 2A (looking down at the top);

FIG. 2C is a plan view at section 34 of the inflatable packerillustrated in FIG. 2A (looking down at the top);

FIG. 2D is a detailed sketch of groove 33 shown in FIG. 2C;

FIG. 3 is a sketch of an element useful in the present invention; and

FIG. 4 is a graphical representation of data showing the benefits of usein the present invention of the element illustrated in FIG. 3;

While the invention will be described in connection with its preferredembodiments, it will be understood that the invention is not limitedthereto. On the contrary, the invention is intended to cover allalternatives, modifications, and equivalents which may be includedwithin the spirit and scope of the present disclosure, as defined by theappended claims.

DETAILED DESCRIPTION OF THE INVENTION

This invention comprises several improvements to an inflatable packerassembly to address performance limitations in existing packer designs.These improvements allow the assembly to operate more reliably when (1)large compressive loads are applied to the packer, (2) large externalpressures are applied to the packer, and/or (3) the packer is placed ina particulate-laden environment.

In the current invention, the compressive load capability is optimizedby maximizing the outer tubular diameter of the mandrel with respect tothe inner diameter of the element. To facilitate load transfer throughthe large-diameter tubular mandrel, the threads at both ends areoriented so as to compress at one quarter of the buckling load therebyallowing the shoulders above and below the threads to shoulder with theadjacent female sub. This feature substantially ensures that the entireload-bearing cross-sectional area is in contact when the tool issubjected to large compressive load.

The tubular mandrel is constructed to be effectively flush with theinner diameter of the element, i.e., the outer diameter of the mandrelis substantially equal to the inner diameter of the element. In oneembodiment, the tubular mandrel has one or more passages therethroughfor the passage of fluid, electrical wires, or other devices though theinterior thereof. Fluid flow passages, e.g., comprising a plurality ofmetal runners to form slots or “flutes”, are provided down the sides ofthe mandrel and/or on the inner-bladder of the element to allow fluidflow along the length of the element while retaining the large outerdiameter required for high resistance to buckling and bending loads. Asused herein, the term “fluid flow passages” includes any passage formedin any way in the annulus between the mandrel and the inner-bladder,such as flutes in the mandrel or inserted tubes, but is not intended torefer to an annular region between the mandrel and the inner bladder.Passages may comprise holes, perforations, grooves, slots, or othercontinuous openings. To reduce the likelihood of damage to theinner-bladder, the fluid entrance to the flutes are preferably orientedparallel to the longitudinal axis of the mandrel to avoid any fluid-jetimpingement on the inner-bladder. Fluid flow through the flutes andannulus is preferably substantially parallel to the longitudinal axis ofthe mandrel; however, some or all of the fluid flow may be oriented toflow in a helical path around the outer surface of the mandrel, or insome other path.

When flutes are used to provide the fluid flow passages, the flutes aredesigned to accommodate external pressure loading without damaging thethin inner-bladder. This is accomplished, for example without limitingthis invention, through the use of chamfered and beveled edges, a slowrun-out at the end of the flutes, and/or the installation of a suitablefilter or screen at the entrance to, throughout and/or covering theflutes. A suitable filter or screen may comprise, for example, a shapedload-bearing, porous material, sintered metal filters, machined screens,and other suitable filters or screens as will be familiar to thoseskilled in the art. The combination of these features minimizes thechance to cut the inner-bladder in the event external pressure forcesthe bladder into the mandrel and mandrel/end-cap junctions.

In addition to resisting higher compressive loads without buckling, thenew, larger mandrel design improves packer performance in other ways; 1)the smaller resultant clearance between the mandrel and the elementminimizes the opportunity for occurrence of inner-bladder pinchingfailures, 2) the design of the mandrel's outer diameter profilemitigates element inner-bladder extrusion failures caused by theapplication of external-pressure, and 3) the proportionately largerinner diameter allows for both significant fluid flow for rapid pressureequalization across the packer and the passage of secondary conduits foradditional communication (pressure, flow, electrical) with the wellboreand remaining bottomhole assembly below the packer.

In one embodiment of the present invention, numerous fine holes aredrilled (via mechanical means, by laser, etc) through the tubularmandrel, each hole preferably having no greater than a 0.8 mm ( 1/32inch) diameter. The hole diameter is then small enough to preventextrusion failures. In this embodiment, enough holes are drilled toallow for adequate inflation and deflation times, as will be familiar tothose skilled in the art.

Referring now to FIG. 2A, in one embodiment of this invention a mandrel20 has an upper end 25 having threads 26, for connection to tubing or anend-cap, and sealant ring glands 42 and 44 to assist in sealing. Neithertubing or an end-cap is shown in any of FIG. 2A-FIG. 2D; any tubing orend-cap that is suitable for the application at hand may be used,although same may require modification to fit mandrel upper end 25, allas will be familiar to those skilled in the art. Further, in thisembodiment mandrel 20 in section 24 has an outer edge 20 c and an outerdiameter 22 of about 5.05 cm. (1.99 inches). Referring to FIG. 2B,mandrel 20 at section 24 has outer edge 20 c and a plurality of flutesor grooves 23 having outer edge 20 a, each having a width 21 of about0.64 cm. (0.25 inches) and a depth 27 of about 0.25 cm. (0.1 inch) andbeing substantially evenly spaced at an angle 29 of about 45 degreesalong the circumference of mandrel 20. Referring again to FIG. 2A,mandrel 20 has a lower end 35 having threads 36, for connection to anend-cap, and sealant ring glands 52 and 54 to assist in sealing, as willbe familiar to those skilled in the art. The end-cap is not shown in anyof FIG. 2A-2D and may be any end-cap that is suitable for theapplication at hand, although same may require modification to fitmandrel lower end 35, as will be familiar to those skilled in the art.Further, mandrel 20 in section 34 has outer edge 20 b and an outerdiameter 32 of about 4.92 cm. (1.937 inches). Referring to FIG. 2C,mandrel 20 at section 34 has outer edge 20 b and a plurality of flutesor grooves 33 having outer edge 20 a, each having a width 31 of about0.64 cm. (0.25 inches) and a depth 37 of about 0.188 cm. (0.074 inch)and being substantially evenly spaced at an angle 39 of about 45 degreesalong the circumference of mandrel 20. Referring now to FIG. 2D, grooves33 in section 34 are manufactured with chamfers 40 at an angle of about45 degrees and are beveled to minimize damage to the inner bladder ofthe inflatable element circumferentially disposed over mandrel 20 whenexposed to external pressure. Preferably, grooves 23 in section 24 (seeFIG. 2B) are similarly chamfered and beveled. This embodiment mayinclude screen sleeves that are disposed axially over the length of thefluted region and are supported against radial external loading by thenon-fluted portion 20 b of mandrel 20 outside diameter. The screensleeves could be confined axially through a diameter upset on themandrel at one end and a removable securing device on the other end, forexample, a threaded sleeve that screws onto mandrel 20 and axiallypresses the screen sleeves against the mandrel diameter upset. Thescreen sleeves would contain numerous radial holes sized to preventextrusion of the inner bladder when external pressure is applied, thenumerous radial holes having diameters of about 0.2 mm (0.008″) andnumbering in the thousands. It may be preferable to make the screensleeve in two or more sections in order to reduce the longitudinaldimension over which tight radial tolerances must be maintained and tofacilitate cleaning and inspection. Reference to a screen herein will beunderstood to include embodiments having such multiple sections. Theinflatable element is not shown in any of FIG. 2A-FIG. 2D and may be anyinflatable element that is suitable for the application at hand, as willbe familiar to those skilled in the art. The specific description ofthis embodiment of the invention in no way limits this invention. As isfamiliar to those skilled in the art, dimensions of parts are adjustedas needed for the application at hand.

In order to accommodate operation of the inflatable packer assemblyaccording to this invention in a particulate-laden fluid, wipers arepreferably added to the floating end to remove particulates as thepacker is inflated and deflated. In addition to the wipers, redundanto-rings seals with back-up rings to prevent extrusion preferably replacethe single o-ring seals commonly used in existing designs. A POLY-PAK,pressure-energized seal is preferably used in the floating end forimproved sealing and a more robust seal for use in particulate-ladenenvironments.

Referring again to FIG. 2A, upper end 25 of tubular mandrel 20 comprisesa blunt nose 43 and threads 26, which threads 26 are oriented so as tocompress at one quarter of the buckling load thereby allowing theshoulders above and below the threads to shoulder with the female subabove, as will be familiar to those skilled in the art. In thisembodiment, threads 26 are oriented at an angle 41 of about 30 degrees.Also, the seal system comprises VITON o-rings (not shown in the FIG.) inring glands 44 with PARBAK backup rings (not shown in the FIG.) in ringglands 42. The tubular or end-cap to which upper end 25 is connected mayrequire modification to ensure a tight fit, as will be familiar to thoseskilled in the art.

Lower end 35 of tubular mandrel 20 comprises a blunt nose 53 and threads36, which threads 36 are oriented so as to compress at one quarter ofthe buckling load thereby allowing the shoulders above and below thethreads to shoulder with the female sub below, as will be familiar tothose skilled in the art. In this embodiment, threads 36 are oriented atan angle 51 of about 30 degrees. Also, the seal system comprises VITONo-rings (not shown in the FIG.) in ring glands 54 with PARBAK backuprings (not shown in the FIG.) in ring glands 52. The end-cap to whichlower end 35 is connected may require modification to ensure a tightfit, as will be familiar to those skilled in the art. When mandrel lowerend 35 is attached to a floating end (end not shown in the FIG.) thefloating end preferably comprises a TEFLON wiper ring and a poly-packpressure energized seal, both as will be familiar to those skilled inthe art.

Additionally, when a packer assembly according to this invention is usedin a particulate-laden fluid, a metal-slat reinforced element ispreferred. Referring now to FIG. 3, one end of a preferred element 60for use in a packer assembly according to this invention is illustratedas attached to an end-cap 66. Prior to inflation, the outer elastomercover 64 has a length 62 of exposed slats 63 of about 7.62 cm. (3.0inches) with a taper 65 of about 15 degrees. Preferably element 60 hassuch exposed slats at both ends.

In an experimental testing program conducted to evaluate the performanceof existing packer/mandrel assemblies and assemblies according to thisinvention, conventional packer/mandrel assemblies buckled and failedunder a compressive load of 378.1 kN (85,000 lbs.) or 34,474 kPa (5000psi) differential. The modified, larger diameter mandrel according tothis invention withstood 458.2 kN (103,000 lbs.) or 41,369 kPa (6000psi) differential with no buckling, and up to 685 kN (154,000 lbs.) or62,053 kPa (9000 psi) differential with slightly bending but no pressurecontainment failure of the packer element.

FIG. 4 compares the deflated outer diameter of a packer according tothis invention without exposure of 3 inches of the slats at each end tothe deflated outer diameter of a packer according to this invention withexposure of 3 inches of slats (as illustrated in FIG. 3) at each end.Each packer was tested within casing having an inner diameter of about11.86 cm (4.67 inches). The element on each packer had an outer diameterof about 9.53 cm (3.75 inches) and a rubber outer cover with a thicknessof about 0.95 cm (⅜ inch). Referring again to FIG. 4, abscissa 70indicates axial position of the packers during testing, with thenumerals 2, 4, 6, . . . 32 indicating inches from the rubber edgenearest the top end. Ordinate 71 indicates the measured outer diameterof the element in inches, area 72 shows measurement data from theoriginal element before the first inflation, area 73 shows measurementdata about the element as modified with the exposed slats after 30inflation/deflation cycles, and area 74 shows measurement data about theoriginal element (unmodified) after 20 inflation/deflation cycles. Themaximum final outer diameter of the packer with the exposed slats wasabout 10.62 cm. (4.182 inches) after 30 cycles compared to a maximumfinal outer diameter of about 11.30 cm. (4.45 inches) after 20 cyclesfor the packer without exposed slats. This reduction in outer diameterincreased the annular flow area by 115% from about 10.2 cm² (1.58inches²) for the original outer cover to about 21.9 cm² (3.39 inches²)for the modified outer cover. The modified packer/mandrel assembly wastested successfully in 20/40 proppant, as will be familiar to thoseskilled in the art, at pressures up to about 55,159 kPa (8,000 psi)without failing. During this experiment, the wiper and improved sealdesigns discussed herein were found to operate successfully inparticulate-laden fluid.

While the present invention has been described in terms of one or morepreferred embodiments, it is to be understood that other modificationsmay be made without departing from the scope of the invention, which isset forth in the claims below.

1. An inflatable packer comprising: (a) a tubular mandrel having alongitudinal axis; (b) an inflatable element substantiallyconcentrically disposed around said tubular mandrel, said inflatableelement having a first end and a second end with each said end beingsealingly attached to said tubular mandrel, and said inflatable elementbeing adapted (i) to be inflated by introduction of pressurized fluidinto an annular space between said inflatable element and said tubularmandrel and (ii) to be deflated by removal of said pressurized fluidfrom said annular space; and (c) one or more fluid flow passagespositioned substantially longitudinally along said tubular mandrel andextending through said annular space between said inflatable element andsaid tubular mandrel, which fluid flow passages are adapted to cause atleast a portion of said pressurized fluid to be introduced into saidannular space in a direction substantially parallel to said longitudinalaxis of said tubular mandrel.
 2. The inflatable packer of claim 1wherein said tubular mandrel has an outer diameter that is substantiallyequal to the inner diameter of said inflatable element prior toinflation.
 3. The inflatable packer of claim 1 wherein at least one ofsaid fluid flow passages is formed by two or more grooves in saidtubular mandrel.
 4. The inflatable packer of claim 1 wherein saidinflatable element comprises an outer elastomeric cover and a pluralityof interconnected inner slats and, further, wherein at least a portionof said outer elastomeric cover has been removed such that at least aportion of said plurality of interconnected inner slats are exposed. 5.An inflatable packer suitable for use under a pre-selected compressiveload, said inflatable packer comprising: (a) a tubular mandrel having alongitudinal axis, and (b) an inflatable element substantiallyconcentrically disposed around said tubular mandrel and adapted toprovide pressure seals above and below said inflatable packer wheninflated, and further said tubular mandrel having an outer diameterconfigured to prevent bending and buckling of said tubular mandrel undersaid pre-selected compressive load that results in failure of either ofsaid pressure seals or of said inflatable packer and said tubularmandrel having one or more fluid flow passages positioned substantiallylongitudinally along said tubular mandrel and extending through anannular space between said inflatable element and said tubular mandrel.6. An inflatable packer suitable for use under a pre-selected externalpressure, said inflatable packer comprising: (a) a tubular mandrelhaving a longitudinal axis; (b) an inflatable element comprising aninner bladder and an outer elastomeric cover and being substantiallyconcentrically disposed around said tubular mandrel, said inflatableelement having a first end and a second end with each said end beingsealingly attached to said tubular mandrel, and said inflatable elementbeing adapted (i) to be inflated by introduction of pressurized fluidinto an annular space between said inflatable element and said tubularmandrel and (ii) to be deflated by removal of said pressurized fluidfrom said annular space; (c) one or more fluid flow passages positionedsubstantially longitudinally along said tubular mandrel and extendingthrough said annular space between said inflatable element and saidtubular mandrel, wherein fluid flow passages are adapted to cause atleast a portion of said pressurized fluid to be introduced into saidannular space in a direction substantially parallel to said longitudinalaxis of said tubular mandrel, and further said tubular mandrel having anouter diameter configured to prevent extrusion of said inner bladderinto one or more of said fluid flow passages in said directionsubstantially parallel to said longitudinal axis of said tubular mandrelwhen said inflatable packer is subjected to said pre-selected externalpressure.
 7. An inflatable packer comprising: (a) a tubular mandrelhaving a longitudinal axis and one or more fluid flow passagespositioned substantially longitudinally along said tubular mandrel, and(b) an inflatable element comprising an inner bladder and an outerelastomeric cover and being substantially concentrically disposed aroundsaid tubular mandrel, said inflatable element having a first end and asecond end with each said end being sealingly attached to said tubularmandrel, and said inflatable element being adapted (i) to be inflated byintroduction of pressurized fluid into an annular space between saidinflatable element and said tubular mandrel and (ii) to be deflated byremoval of said pressurized fluid from said annular space, and furthersaid tubular mandrel having an outer diameter configured to preventfolding of said inner bladder within said annular space between saidinflatable element and said tubular mandrel.
 8. An inflatable packercomprising: (a) a tubular mandrel having a longitudinal axis and one ormore fluid flow passages positioned substantially longitudinally alongsaid tubular mandrel, and (b) an inflatable element comprising an outerelastomeric cover and a plurality of interconnected inner slats andbeing substantially concentrically disposed around said tubular mandrel,said inflatable element having a first end and a second end with eachsaid end being sealingly attached to said tubular mandrel, and saidinflatable element being adapted (i) to be inflated by introduction ofpressurized fluid into an annular space between said inflatable elementand said tubular mandrel and (ii) to be deflated by removal of saidpressurized fluid from said annular space, and further wherein at leasta portion of said elastomeric cover has been removed such that anappropriate length of said plurality of interconnected inner slats areexposed to minimize the deflated diameter of said inflatable element andto prevent loss of said outer elastomeric cover when said inflatablepacker undergoes a plurality of inflation/deflation cycles.
 9. Aninflatable packer suitable for use under a pre-selected internalpressure, said inflatable packer comprising: (a) a tubular mandrelhaving a longitudinal axis and one or more fluid flow passagespositioned substantially longitudinally along said tubular mandrel, and(b) an inflatable element comprising an outer elastomeric cover, aninner bladder, and a plurality of interconnected inner slats and beingsubstantially concentrically disposed around said tubular mandrel, saidinflatable element having a first end and a second end with each saidend being sealingly attached to said tubular mandrel, and saidinflatable element being adapted (i) to be inflated by introduction ofpressurized fluid into an annular space between said inflatable elementand said tubular mandrel and (ii) to be deflated by removal of saidpressurized fluid from said annular space, and further, wherein aportion of said outer elastomeric cover has been removed such that anappropriate length of said plurality of interconnected inner slats areexposed to prevent said exposed plurality of interconnected inner slatsfrom damaging said inner bladder when said inflatable packer issubjected to said pre-selected internal pressure.
 10. An inflatablepacker suitable for use under a pre-selected external pressure, saidinflatable packer comprising: (a) a tubular mandrel having alongitudinal axis; (b) an inflatable element comprising an inner bladderand an outer elastomeric cover and being substantially concentricallydisposed around said tubular mandrel, said inflatable element having afirst end and a second end with each said end being sealingly attachedto said tubular mandrel, and said inflatable element being adapted (i)to be inflated by introduction of pressurized fluid into an annularspace between said inflatable element and said tubular mandrel and (ii)to be deflated by removal of said pressurized fluid from said annularspace; (c) one or more fluid flow passages positioned substantiallylongitudinally along said tubular mandrel and extending through saidannular space between said inflatable element and said tubular mandrel,wherein fluid flow passages are adapted to cause at least a portion ofsaid pressurized fluid to be introduced into said annular space in adirection substantially parallel to said longitudinal axis of saidtubular mandrel, and wherein at least one of said fluid flow passageshas at least one edge that is chamfered at an angle of about 40 degreesto about 50 degrees.
 11. An inflatable packer suitable for use under apre-selected external pressure, said inflatable packer having a fixedend and a floating end and comprising: (a) a tubular mandrel having alongitudinal axis; (b) an inflatable element comprising an inner bladderand an outer elastomeric cover and being substantially concentricallydisposed around said tubular mandrel, said inflatable element having afirst end and a second end with each said end being sealingly attachedto said tubular mandrel, and said inflatable element being adapted (i)to be inflated by introduction of pressurized fluid into an annularspace between said inflatable element and said tubular mandrel and (ii)to be deflated by removal of said pressurized fluid from said annularspace; (c) one or more fluid flow passages positioned substantiallylongitudinally along said tubular mandrel and extending through theannular space between said inflatable element and said tubular mandrel,which fluid flow passages are adapted to cause at least a portion ofsaid pressurized fluid to be introduced into said annular space in adirection substantially parallel to said longitudinal axis of saidtubular mandrel; and (d) at least one device adjacent said fixed end,said device being adapted to prevent extrusion of said inner bladderinto one or more of said fluid flow passages in a directionsubstantially parallel to said longitudinal axis of said tubular mandrelwhen said packer is subjected to said pre-selected external pressure.12. The inflatable packer of claim 3, further comprising a screen in theform of a cylindrical sleeve sized to fit around said tubular mandrel,said screen having holes to allow fluid flow but prevent extrusion ofsaid inflatable element during deflation of said inflatable packer. 13.The inflatable packer of claim 12, wherein said screen sleeve isconfined on said tubular mandrel axially by a diameter upset on saidtubular mandrel at one end, and a removable securing device at the otherend.
 14. A method comprising: providing an inflatable packer comprisinga tubular mandrel having a longitudinal axis and one or more fluid flowpassages positioned substantially longitudinally along said tubularmandrel, and an inflatable element substantially concentrically disposedaround said tubular mandrel, said inflatable element having a first endand a second end with each said end being sealingly attached to saidtubular mandrel, and said inflatable element being adapted (i) to beinflated by introduction of pressurized fluid into an annular spacebetween said inflatable element and said tubular mandrel and (ii) to bedeflated by removal of said pressurized fluid from said annular space;and disposing said inflatable packer into a wellbore.
 15. The method ofclaim 14, wherein said one or more fluid flow passages are adapted tocause at least a portion of said pressurized fluid to be introduced intosaid annular space in a direction substantially parallel to saidlongitudinal axis of said tubular mandrel.
 16. The method of claim 14wherein said tubular mandrel has an outer diameter that is substantiallyequal to the inner diameter of said inflatable element prior toinflation.
 17. The method of claim 14 comprising defining at least oneof said fluid flow passages to be formed by two or more grooves in saidtubular mandrel.
 18. The method of claim 14 wherein said inflatableelement comprises an outer elastomeric cover and a plurality ofinterconnected inner slats and, further, wherein at least a portion ofsaid outer elastomeric cover has been removed such that at least aportion of said plurality of interconnected inner slats are exposed. 19.The method of claim 18 comprising configuring a portion of said outerelastomeric cover has been removed such that an appropriate length ofsaid plurality of interconnected inner slats are exposed to prevent saidexposed plurality of interconnected inner slats from damaging said innerbladder when said inflatable packer is subjected to said pre-selectedinternal pressure.
 20. The method of claim 14 comprising configuringsaid inflatable packer to have an outer diameter suitably large toprevent bending and buckling of said tubular mandrel under saidpre-selected compressive load that results in failure of either of saidpressure seals or of said inflatable packer.
 21. The method of claim 14comprising configuring said tubular mandrel to have having an outerdiameter suitably large to prevent extrusion of said inner bladder intosaid one or more of said fluid flow passages in said directionsubstantially parallel to said longitudinal axis of said tubular mandrelwhen said inflatable packer is subjected to said pre-selected externalpressure.
 22. The method of claim 14 wherein at least one of said fluidflow passages has at least one edge chamfered at an angle of about 40degrees to about 50 degrees.
 23. The method of claim 14 comprisingexpanding said inflatable packer to seal a portion of said wellbore. 24.The method of claim 23 comprising producing hydrocarbons from saidwellbore by utilizing said expanded inflatable packer.